1. Field of the Invention
The present invention relates to a tandem waterwheel type trommel apparatus for recovering aggregates such as sand and gravel from returned concrete remaining in a concrete mixer truck after discharge of freshly mixed concrete at a building site and from waste water after washing the mixer of the concrete mixer truck (which materials are generically called as sludge)
2. Description of the Related Art
This kind of trommel apparatus includes various well-known various types of trommel apparatuses: (A) one in which coarse aggregates such as sand and gravel are separated by a rotating cylindrical wire netting, and sand is thereafter scooped up by a screw conveyor from sludge containing sand, (B) one in which a cylindrical wire netting is rotatably disposed in a laterally-disposed semicylindrical bath fixed on a base and having an inside diameter larger than the diameter of the cylindrical wire netting, and an inner screw and an outer screw are disposed along the inner and outer surfaces of the cylindrical wire netting to form a classifying drum, the inner screw being formed so as to move coarse aggregates such as gravel to a rear outlet, and in which the outer screw is operated to run sand into a rear accumulation section, and this sand is scooped up and discharged out of the bath by scooping blades, and (c) one in which an internal space of a laterally-disposed rotating cylindrical drum is partitioned by doughnut partition plates to form a mix-washing bath, an overflow transport bath and a trommel bath in the order from the upstream side, and in which sludge is thrown into the mix-washing bath to be mixed and washed, sand and gravel are scooped up by scoop blades and supplied to the trommel bath to be separated, and remaining water is caused to overflow into the overflow transport bath and is returned to the mix-washing bath by buckets (an invention made by the inventor of the present invention, U.S. Pat. No. 5,082,553).
Another type of trommel apparatus has been invented by the inventor of the present invention and an application for it has been filed with the Japanese Patent Office (Japanese Patent Application No. Hei 2-418802) which consists of (D) a combination of a trommel for separating coarse aggregates such as gravel and another trommel for separating fine aggregates such as sand, which are disposed on the same base with a certain difference in level set therebetween, whereby two-stage classification of sludge is made.
The trommel apparatuses (A) and (B), however, are of a one-bath type such that sludge is directly flows into a bath for separating sand and gravel, wherein a trommel is incorporated and aggregates classified thereby are scooped up and moved out of the surface of sludge by scoop-up blades or the like. Accordingly, if returned concrete is supplied, the sludge concentration becomes so high that a substantially large amount of cement component is attached to recovered aggregates. Aggregates in such a state cannot be directly reused. Moreover, a washing water discharged from a concrete mixer truck flows directly into such a one-bath trommel to cause a large change in flow rate, while the trommel in the both is constantly rotated. The inflow is therefore disturbed at the time of discharge from the mixer truck, so that fine sand is drawn into waste water to flow out through a drain port, resulting in failure to recover fine sand.
The trommel apparatus (C) is of a two-bath type such that sludge flows into a mix-washing bath, and aggregates are scooped up therein with blades to enter a trommel bath and are classified and rinsed by a trommel incorporated in this bath. Recovered aggregates can be thereby washed with water sufficiently. However, the two baths are rotated integrally with each other, the flow in the mix-washing bath is disturbed, so that fine sand cannot be suitably recovered. There is also a problem of difficulty in maintenance, e.g., in removing a clog in the trommel since the trommel is incorporated in a cylinder.
The trommel apparatus (D) is a tandem waterwheel type trommel in which coarse aggregates are recovered in the first bath, sludge is successively scooped up by waterwheel buckets to cause aggregates to settle in each bucket, and water is drained off as overflowing water. It is therefore possible to reliably recover fine sand. However, no water washing step is provided, as in the case of the types (A) and (B).
In view of the above-described drawbacks of the conventional art, an object of the present invention is to provide a trommel apparatus capable of sufficiently washing recovered aggregates with water as well as completely recovering fine sand.
Another object of the present invention is to provide a trommel apparatus capable of recovering aggregates reusable as freshly mixed concrete by resupplying water at a smaller rate.
Still another object of the present invention is to provide a trommel apparatus capable of suitably processing mixer truck washing water and returned concrete simultaneously.